Report on the Bacteriology of Water. 529 



either the unsterile Thames or Loch Katrine waters, although 

 it was precisely in the deep well water that the water bacteria 

 underwent multiplication. 



(8.) These experimental observations lead me to the conclusion 

 that the antagonistic action of the unsterile waters on the 

 typhoid bacillus is not to be attributed to the multiplication 

 of the water bacteria leading to the suppression of the typhoid 

 bacilli " by competition in the struggle for existence," to use 

 the common phraseology of many writers on these subjects, 

 but through the existence in the unsterile waters of conditions 

 (due, doubtless, to a great extent to the presence of chemical 

 products elaborated by water bacteria) which are inimical to 

 the vitality of the typhoid bacillus. 



That conditions inimical to the vitality of the typhoid bacillus can 

 be generated by the water bacteria alone is demonstrated by the above 

 experiments in which a few drops of unsterile Thames water were 

 added to the typhoid-infected steam-sterilised water, with the result 

 that the longevity of the typhoid bacilli in this water was far less 

 than in the steam-sterilised water itself. 



That the longevity of the typhoid bacillus is still less in the natur- 

 ally unsterile water than in that rendered unsterile by inoculation, I 

 attribute to the fact that in the naturally unsterile Thames water, 

 countless generations of water bacteria have flourished before the 

 water is made the subject of experiment at all, and it must, therefore, 

 be more or less saturated with those bacterial products which are 

 prejudicial to the vitality of the typhoid bacillus, and which, in fact, 

 frequently hamper or even inhibit the further multiplication of the 

 water bacteria themselves. 



The deep well water, on the other hand, in its natural condition is 

 in a very different state ; as my numerous former examinations (see 

 Second Report, pp. 178 180) of this water have shown, it is drawn 

 from its subterranean source in an almost perfectly sterile condition, 

 having never since its exhaustive filtration through the porous strata of 

 the earth, in which it has altogether altered its chemical composition, 

 harboured any micro-organisms at all, so that the abundant bacterial 

 multiplication, which, as I have shown, it exhibits in the laboratory, 

 is really the first time that it is subjected to the influence of bacterial 

 growth, and it takes a correspondingly longer time, therefore, for the 

 conditions inimical to the typhoid bacillus to be established. In fact, 

 in the experiments with deep well water (see pp. 505, 515) the 

 typhoid bacillus was actually discovered in the unsterile water a little 

 later than in the steam-sterilised water. That the multiplication of the 

 bacteria in the deep well water does not lead to conditions so antago- 

 nistic to the vitality of the typhoid bacillus is also, no doubt, attri- 



